This is a study of the role of connective tissues in the regulation of development of the bronchial tree in the early embryonic rat and chick lung. Development of the lung in vivo will be compared to that which occurs in organ cultures of lung buds grown on a nutrient agar substrate. The relationship between bronchial development and the types and relative proportions of collagen, proteoglycans, fibronectin and basement membranes will be studied with light and electron microscopy, immunofluorescence, immuno-scanning and transmission electron microscopy, autoradiography, and biochemical analyses. The effects of microenvironmental factors such as oxygen concentration, pH, specific ion concentrations, components of the nutrient medium and various pharmacologic agents on lung development will be determined. These studies will help us to understand the role of connective tissues in the regulation of bronchial morphogenesis and lung development.